Low back pain is a major cause of industrial disability and a significant cause of functional impairment and outpatient medical care. We propose a randomized, controlled, single blind clinical trial of rotatory manipulation of the lumbar spine in cases of acute low back pain. Approximately 400 patients from The Wellesley Hospital Outpatient Clinics and certain private practices will be interviewed, have lumbar spine x-rays, and be examined by an Assessor who will note subjectve and objective criteria of pain and impairment. Patients will then be treated according to a randomized schedule either by physiotherapy alone (massage or faradic stimulation) or by physiotherapy plus manipulation by a trained manipulator. Patients will return four times at increasing intervals; each time they will be evaluated by the Assessor who is "blind" to the type of treatment the patient is receiving. Results will be examined in terms of disability days and subjective and objective quantitative measures of impairment. We hope to show that manipulation, if done under proper indications, will contribute to a greater reduction of back pain morbidity than can physiotherapy alone.